Volcanism in Germany can be traced back for millions of years, due to the collision between the African and Eurasian plates, but it has been concentrated in bursts associated with the loading and unloading of ice during glacial advances and retreats. The initial blasts of Laacher See, which took place in late spring or early summer, flattened trees up to four kilometres away. The magma opened a route to the surface which erupted for about ten hours, with the plume probably reaching a height of 35 kilometres. Activity continued for several weeks or months, with pyroclastic currents which covered valleys up to ten kilometres away with sticky tephra. Near the crater deposits are over fifty metres, and even five kilometres away they are still ten metres thick. All plants and animals for a distance of about sixty kilometres to the northeast and forty kilometres to the southeast must have been exterminated.[6]
An estimated 6 km3 (1.4 cu mi) of magma erupted,[7] producing around 16 km3 (3.8 cu mi) of tephra.[8] This 'huge' Plinian eruption thus had a Volcanic Explosivity Index (VEI) of 6.

Tephra deposits from the eruption dammed the Rhine, creating a 140 km2 (50 sq mi) lake. When the dam broke, an outburst flood swept downstream, leaving deposits as far away as Bonn.[7] The fallout has been identified in an area of more than 300,000 square kilometres, stretching from central France to northern Italy, and from southern Sweden to Poland, making it an invaluable tool for chronological correlation of archaeological and palaeoenvironmental layers across the area.[9]

The wider effects of the eruption were limited, amounting to several years of cold summers and up to two decades of environmental disruption in Germany. However, the lives of the local population, known as the Federmesser culture, were disrupted. Before the eruption, they were a sparsely distributed people who subsisted by foraging and hunting, using both spears and bows and arrows. According to archaeologist Felix Riede, after the eruption the area most affected by the fallout, the Thuringian Basin occupied by the Federmesser, appears to have been largely depopulated, whereas populations in southwest Germany and France increased. Two new cultures, the Bromme of southern Scandinavia and the Perstunian of northeast Europe emerged. These cultures had a lower level of toolmaking skills than the Federmesser, particularly the Bromme who appear to have lost the bow and arrow technology. In Riede's view the decline was a result from the disruption caused by the Laacher See volcano.[10]